The claim term, “support surface,” was ambiguous in the claim as to when the “slide” must be supported. The specification resolved the ambiguity in favor of the District Court’s construction. The patentee’s proposed construction was not identified in the specification and the doctrine of claim differentiation was not applicable, because the court’s construction did not give claim 1 the same scope as claim 6. The prosecution history further was not clear enough to change the meaning of the claim term.